The present invention relates to transparent polyamide compositions having high resistance to chemical agents, as well as to the process for their preparation and the articles obtained from said compositions.
Those polyamides, as well as their alloys, are widely used for numerous applications. Some of these applications require specific properties. Amongst these desired properties mention may be made of the impact strength, the tensile strength and/or the compressive strength, that is to say the mechanical properties. Other desired properties are the transparency and the high resistance to chemical agents in order to resist atmospheric agents over time. Numerous articles require a transparent appearance, a high resistance to chemical agents and good mechanical properties. Bottles, stoppers, spectacle frames and others may be mentioned by way of example.
There is therefore, a current need to have available said transparent materials having a high resistance to chemical agents.
Numerous homopolyamides and copolyamides, both amorphous and crystalline, have therefore been proposed. Similarly, the mixtures or alloys of the latter have been proposed. These alloys consist of a transparent amorphous copolyamide mixed with crystalline (co)polyamide. The aim of these alloys is to obtain a reduction in the production cost and/or an improvement in the resistance to chemical agents.
Thus, JP-60-215053 and 60-214054 (KOKAI) describe and claim alloys comprising, on the other hand, a transparent polyamide and, on the other hand, a crystalline polyamide. The transparent polyamide consists of aliphatic units as an essential monomer component, chosen from lauryl lactam, 12-aminododecanoic acid or 11-aminoundecanoic acid, and cyclic units. The examples gtiven for these transparent polyamides reveal a cycloaliphatic diamine, bis-(4-aminocyclohexyl)methane, and an aromatic diacid, isophthalic acid, as cyclic units. The crystalline polyamide consists of polyamide-12 and/or -11, or of copolyamide having a 12 and/or 11 unit as essential monomer. The mixing conditions are not specified; it is merely indicated that any known process can be used. The resulting compositions are transparent.
FR-A-2,575,756 and FR-A-2,606,416 describe and claim mixtures or alloys similar to those mentioned above. Again, in this case, isophthalic acid is the predominant aromatic diacid component and the mixing conditions are not specified. The mixtures or alloys obtained are transparent.
The mixture of polyamides as used in the cases cited above meets the conditions imposed by the products to be mixed. Thus, U.S. Pat. No. 4,404,317 describes the mixing conditions, such as the temperature, for diverse polyamides; in partaicular, it is recommended not to exceed 300.degree. C. because of the degradation of the crystalline polyamide as well as of the amorphous polyamide. In particular, in the "Technical Data Sheet" notice relating to the transparent polyamide Grilamid.RTM. TR 55 which consists of a lauryl lactam unit, isophthalic acid as aromatic diacid and bis-amine A as cycloaliphatic diamine, it is specified that the injection moulding and extrusion temperatures are from 280.degree. to 305.degree. C. and from 270.degree. to 286.degree. C., respectively. Moreover, it is known that crystalline polyamides (including PA12 or PA6,12) have a degradation temperature of the order of 270.degree., both for injection moulding and for extrusion, which may be applied for very short times or in the presence of a stabilizer at a temperature of about 300.degree. C. This is described in the HULS "Engineering Thermoplastics" technical note, on page 65.
EP-A-0 313 436 (in the name of Applicant) describes transparent polyamides in which, on the other hand, terephthalic acid is the predominant aromatic diacid component. These amorphous transparent polyamides have surprising properties both in respect of mechanical properties and in respect of the resistance to chemical agents. Unfortunately, the mixing of these amorphous transparent polyamides with a crystalline polyamide under the conventional conditions mentioned above leads to a composition which is not transparent.
Thus, the desired alloys of these transparent polyamides having improved properties are not transparent if they are produced under normal conditions, and a temperature which is too high would lead to the degradation of the polymers.